Recently, as technology of a display device and a solar cell progresses, demand for a transparent electrode used for the display device and the solar cell rapidly increases. An indium tin oxide (ITO) is generally to a material of the transparent electrode because the ITO is suitable for a mass production technique and for being used for the display device and the solar cell. However, a manufacturing cost of the ITO electrode is very high due to a vacuum process, and the ITO electrode is not stable to an external shock such as a thermal shock. Thus, a material replacing the ITO electrode is developing.
For materials replacing the ITO electrode, there are conductive polymers such as carbon nanotube (CNT), graphene, a zinc oxide (ZnO), poly(3,4-ethylenedioxythiophene) (PEDOT), and so on, a metal nanowire, and the like.
The metal nanowire, more particularly, a silver nanowire among them has a high chemical stability. The silver nanowire has properties of silver having high thermal conductivity and high electric conductivity and an optical property being transparent induced by the nanowire having a very small size. Thus, the metal nanowire, more particularly, the silver nanowire is in the spotlight as a metal material for manufacturing a transparent conductive film. The silver nanowire may be widely applied to electronic, magnetic, and optical elements or devices and sensors, such as, a plasma display panel (PDP), an optical filter, an electromagnetic wave shield, an organic Light emitting diode (OLED), a solar cell, a liquid crystal display (LCD), a touch screen, an EL key pad for a cellular phone, and so on for the future.
The metal nanowire may be manufactured by a synthesizing method, known as a polyol method. In the polyol method, the metal salt is reduced to a metal atom by a polyol solvent (refer to US Laid-open Patent Publication No. 2005/0056118). Generally, the reduced metal atom initially forms seeds through a homogeneous nucleation process. And then, some of seeds grows in all direction in the solution and forms isotropic nano-structures (nanoparticles), and other seeds firstly grows according to a direction of a side surface and forms anisotropic nano-structures (nanotubes, nanowire portions, nano-belts, nanowires, and so on).
Recently, several studies for a flexible-substrate conductor using a metal nanowire are continued and a commercialization thereof is achieved to some agree. However, an electric resistance at contact points between nanowires may increase due to sulfidation and an oxidation, and an electric property may be bad. Thus, it may be a fatal defect for a device where reliability is needed.
In the past, studies for increasing an electric conductivity and reducing a haze were progressed, considering that the metal nanowire is used for a conductive material of a display device. However, a study for increasing light-scattering to have light extraction was not suggested.